The present invention concerns an oscillating damper of the kind comprising:
a housing defining a chamber filled with damping fluid,
a mobile oscillating plate inside the aforementioned chamber and placed so as to divide the chamber into two sections of variable volume, and
at least one passage created in the oscillating plate to enable the fluid to pass from one section to the other during the motion of said plate.
The present invention is characterized by the fact that the damping fluid is a magneto-rheological or electro-rheological fluid and by the fact that an electrically-controlled excitation device is provided in correspondence with the aforementioned passage in order to control the flow resistance of the fluid passing through said passage.
The compositions of magneto-rheological or electro-rheological fluids undergo a change in apparent viscosity in the presence of a magnetic or electric field. Magneto-rheological fluids generally contain ferromagnetic or paramagnetic particles, typically with a diameter of the order of 0.1 xcexcm, dispersed in a carrier fluid. In the presence of a magnetic field, these particles become polarized and organize themselves into chains of particles within the fluid. These chains of particles have the effect of increasing the fluid""s apparent viscosity or global outflow resistance. In the absence of any magnetic field, the particles return to their disorganized or free state and the apparent viscosity or outflow resistance of the material is correspondingly reduced. Magneto-rheological materials have a controllable behavior that is similar to the one observed in electro-rheological materials, which respond to an electric field instead of a magnetic one.
Both electro-rheological and magneto-rheological materials are useful in providing variable damping forces inside devices such as shock absorbers and elastomeric bearings.
Currently-known magneto-rheological dampers are typically of the type comprising a cylinder and a piston. These dampers have relatively high working pressures (around 30 bar) and must be fitted with sealing elements on the piston rod. Magneto-rheological or electro-rheological fluids are abrasive and the dampers using such fluids tend to have leakage problems.
An oscillating damper made according to the present invention enables a reduction in the working pressure (e.g. 10 instead of 30 bar) with respect to a cylinder and piston damper of comparable features and consequently poses fewer problems from the point of view of fluid leakage.
Another important advantage of the damper made according to the present invention is that the fluid is subject to lower outflow velocities than those occurring in a cylinder and piston type of damper and this enables the damping characteristics to be controlled more easily and accurately.